The chief executive of EADS, Tom Enders, has dismissed fears that the European aerospace group's proposed €34bn merger with UK arms manufacturer BAE Systems will lead to widespread redundancies in the UK, saying that cutting thousands of jobs is "not the purpose" of the deal.

Enders said the combination of Britain's largest defence contractor with the owner of Airbus – which between them employ more than 50,000 in the UK – will "not go down in history as the deal with the most cost synergies." The UK government, which could block the deal, is seeking assurances on jobs and Britain's share of manufacturing work under the new company before giving the merger its blessing

Speaking at a lecture at the Royal Academy of Engineering in London, Enders said: "We have faced the same concerns in France, Germany, over here: does it mean are you guys slashing thousands of jobs etc? That's not the purpose." Enders added that the deal was about creating growth and would be "great for Britain."

Earlier in the day a major shareholder in EADS has had added further complication to the proposed merger by urging the Franco-German industrial group to re-examine the terms of an "unsatisfactory" deal.

The intervention of Lagardère, which owns 7.5% of EADS, added a financial dimension to a transaction that has largely been dominated by political concerns. The combination needs the approval of the British, French, German and US governments, the latter being BAE's largest and most politically sensitive customer.

Lagardère, a conglomerate whose interests span publishing and airport retail, released a statement criticising the terms of the tie-up, in which EADS shareholders will emerge with 60% of the business while BAE stockholders take 40%.

Describing the terms of the merger as "currently unsatisfactory", a spokesman said: "Lagardère calls on the management of EADS to undertake, without delay, the indispensable re-examination of the project to combine EADS and BAE, to better take into account the interest of all the French controlling shareholders of EADS."

Lagardère's chief executive, Arnaud Lagardère, is also the chairman of EADS.

There has been speculation that the French government wants to see ownership shared evenly between Paris, London and Berlin, which would leave BAE shareholders with 33% of the dual-listed business. But it is understood that BAE and EADS are not prepared to alter the balance of the new company's ownership.

Enders said he was relaxed about Lagardère's intervention. "Shareholders are obviously always potentially concerned. They invest to make money so it's not surprising that some shareholders are concerned about the return they are getting."

According to reports, Germany and France are preparing to demand direct stakes of 9% in the merged group. Under the current EADS structure Lagardère and the French state holding company, Sogepa, own 22.35% of EADS, while Germany's national interest is represented by a 22.35% stake held by carmaker Daimler. The UK government, which has a golden share in BAE that allows it to block a non-UK shareholder taking a significant stake, has voiced concerns over the impact on 52,000 manufacturing jobs in Britain but has signalled that it is broadly in favour of the merger. A source close to the deal said the companies had done "everything that they need to do" to meet a 10 October deadline to agree terms, as required by the UK Takeover Panel, but governmental wrangling is now the main issue.

Another source said both sides need the UK, German and French governments to reach agreement before anything is put to shareholders: "Until we have government support or approval for the basic structure, we don't have a deal that we can put to shareholders. Britain's largest trade union, Unite, voiced support for the deal. Ian Waddell, Unite's national officer for aerospace and shipbuilding, said BAE had to reduce its dependence on shrinking US and UK defence budgets. "I don't see a rosy picture going forward. I see the possibility of terminal, and potentially ignominious decline."

Ben Wallace, the Conservative MP whose Lancashire constituency includes the BAE aircraft manufacturing site at Warton, Lancashire, said: "The question nobody seems to know the answer to is, how does this help the company commercially? I can see how it benefits EADS, because it wants to divest itself of the control of the French and German governments. But I do not see how this benefits BAE."

BAE and EADS declined to comment. However, the companies' chief executives made a renewed declaration of the deal's merits on Monday morning in a joint op-ed piece published in the UK, France and Germany.

Ian King, the BAE chief executive, and Enders said: "With the necessary political will and support, management determination, and proper governance, BAE Systems and EADS can produce a whole that is greater than the sum of its parts. Together, we would become a business with a global footprint, and a wider customer base.

"We would be able better to ride the cycles of civil aviation demand and defence spending. And we would be a business with the scale and stability to invest more in R&D, and a force for greater competition and growth. All of this would deliver tangible benefits to our customers in each of the defence, aerospace and security worlds."

BAE and EADS are working to a deadline of 10 October deadline to thrash out a deal. Enders and King indicated that the deal would end Paris and Berlin's dominance of EADS.